This invention relates to a biodegradable barrier film and to disposable absorbent pads, such as sanitary napkins or diapers, for absorbing and retaining body fluids and exudates and utilizing the biodegradable barrier film to prevent the spread of said body fluids.
Disposable absorbent products, such as sanitary napkins, comprise a fibrous body of one or more layers of highly absorbent fibers, usually wrapped within a fluid-permeable cover which may comprise a woven or nonwoven fabric. In addition, such products usually contain a fluid impervious barrier layer to prevent the spread of the menstrual, or other body fluid to the clothing of the wearer.
Both the fibrous body and the fluid-permeable cover are usually cellulosic in nature and are therefore biodegradable and capable of decomposition within a conventional sewage disposal system. The fluid impervious barrier on the other hand is usually made of a water-repellent synthetic polymer, such as polyethylene, which is non-biodegradable and retains its structural integrity even after prolonged exposure to the sewage disposal process. Undegraded plastic film barriers in a sewage system impede the free flow of sewage fluids and impair the functioning of the system.
To provide the desired biodegradability in sanitary napkins, diapers and other disposable absorbent products, it has been proposed to make the barrier films for these products out of biodegradable materials. U.S. Pat. No. 3,602,225 of Edward A. Wielicki, teaches the use of barrier films made of plasticized regenerated cellulose films. My U.S. Pat. No. 3,683,917, teaches the use of barrier films comprising a cellulosic tissue material treated with a water-repellent material. Barrier films made of biodegradable materials have not been used extensively because of their expense and because of the limited range of properties available in such films.
In accordance with one aspect of the present invention, a biodegradable barrier film which comprises a biodegradable material homogeneously dispersed in a matrix of a non-biodegradable film-forming material which is resistant to solubility in water, the biodegradable material being present in said film material in an amount from about 40 to about 60 percent by weight based on the total weight of said biodegradable and said non-biodegradable film-forming material in said film. A plasticizer is preferably incorporated into the film in amounts up to 60 percent by weight based on the entire weight of the film.
The barrier film is impervious to fluid discharge by reason of the film-forming matrix material which is resistant to solubility in water. In barrier films intended for diapers, and in other applications in which the barrier film is likely to come into contact with a relatively large volume of a highly fluent discharge, the film-forming material is preferably a water-insoluble material capable of forming a coherent self-supporting film.
In barrier films intended for sanitary napkins, and in other applications in which the barrier film is likely to come into contact with a smaller volume of a less fluent, or mucilaginous discharge, the film material need not be water-insoluble but can be slowly soluble in water provided it is in a self-supporting film of sufficient thickness to maintain its integrity during the functioning of the absorbent pad. Suitable film-forming materials include polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, high molecular weight polyvinyl pyrrolidone and polyvinyl alcohol.
The biodegradable material used in the barrier film of this invention is a finely divided material which is preferably a material which swells in water. Suitable biodegradable materials include carbohydrates such as starch, finely divided regenerated cellulose, starch dextrin and natural gums, such as gum acacia and gum tragacanth; natural resins, such as rosin; proteins such as collagen; and alginates.
When the biodegradable and non-biodegradable materials are present in the film of this invention in the proportions described herein, the film functions as a barrier to body discharge fluids with the essential physical properties of the non-biodegradable film-forming material includes effective resistance to the passage therethrough of the fluids. The film is, however, degradable in sewage systems within the time that sewage is usually treated in such systems, as now to be explained. Without being bound to any theory of operation, it is believed that the biodegradable material is degraded by the action of bacteria in the sewage system and that this degradation is of a continuous character and continues until it creates weakened portions, and ultimately voids the structure of the film. In time the degraded film can no longer maintain its integrity and it breaks down into many pieces, small enough to be handled by normal sewage systems. When the proportion of biodegradable material is in excess of the specified range, the amount of film-forming material is insufficient to provide the necessary strength and other physical properties required in the film of the invention. Conversely, when the proportion of biodegradable material is below the specified range, the breakdown of the film will not be fast enough and/or extensive enough to provide the disintegration of the film into the small particles required for handling by the sewage system.
The films of the invention may be prepared by various methods, depending on the nature of the non-biodegradable film-forming material. A preferred method of preparing the barrier film of the invention when the film-forming material is polyvinyl alcohol is by casting the film from an aqueous dispersion of film-forming material, biodegradable material and plasticizer and then driving off the water. The thickness of the film suitable for use in this invention is dependent on the nature of the materials used. The films should be thick enough to provide the necessary strength and water barrier and should be thin enough to provide the necessary flexibility and to avoid unnecessary expense. The films generally range from about one to two mils in thickness but may be as thin as 1/2 mil, or as thick as about 4 mils, if desired.